Effect of pressure in the growth reactor on the properties of the active region in the InGaN/GaN light-emitting diodes

International audienceEffect of pressure in the reactor in the case of growth of active regions in the InGaN/GaN light-emitting diodes by the method of vapor-phase epitaxy from metalorganic compounds on their electroluminescent and structural properties has been studied. It is shown that, as pressure is increased, the InGaN layers become transformed from being continuous in the lateral direction to the layers of separate InGaN islands. This transformation affects both the emission efficiency and the dependence of efficiency on current

InGaN/GaN heterostructures grown by submonolayer deposition

International audienceInGaN/(Al,Ga)N heterostructures containing ultrathin InGaN layers, grown by submonolayer deposition are studied. It is shown that significant phase separation with the formation of local In-enriched regions ∼3–4 nm in height and ∼5–8 nm in lateral size is observed in InGaN layers in the case of InGaN and GaN growth by cyclic deposition to effective thicknesses of less than one monolayer. The effect of growth interruption in a hydrogen-containing atmosphere during submonolayer growth on the structural and optical properties of InGaN/(Al,Ga)N heterostructures is studied. It is shown that these interruptions stimulate phase separation. It is also shown that the formation of In-enriched regions can be controlled by varying the effective InGaN and GaN thicknesses in the submonolayer deposition cycles

Colour management of InGaN/GaN based monolithic two-wavelength LEDs

The recent advancement in the growth technology of InGaN/GaN has decently positioned InGaN based white LEDs to leap into the area of general or daily lighting. Monolithic white LEDs with multiple QWs were previously demonstrated by Damilano et al. [1] in 2001. However, there are several challenges yet to be overcome for InGaN based monolithic white LEDs to establish themselves as an alternative to other day-to-day lighting sources [2,3]. Alongside the key characteristics of luminous efficacy and EQE, colour rendering index (CRI) and correlated colour temperature (CCT) are important characteristics for these structures [2,4]. Investigated monolithic white structures were similar to that described in [5] and contained blue and green InGaN multiple QWs without short-period superlattice between them and emitting at 440 nm and 530 nm, respectively. The electroluminescence (EL) measurements were done in the CW and pulse current modes. An integration sphere (Labsphere “CDS 600” spectrometer) and a pulse generator (Agilent 8114A) were used to perform the measurements. The CCT and Green/Blue radiant flux ratio were investigated at extended operation currents from 100mA to 2A using current pulses from 100ns to 100μs with a duty cycle varying from 1% to 95%. The strong dependence of the CCT on the duty cycle value, with the CCT value decreasing by more than three times at high duty cycle values (shown at the 300 mA pulse operation current) was demonstrated (Fig. 1). The pulse width variation seems to have a negligible effect on the CCT (Fig. 1). To account for the joule heating, a duty cycle more than 1% was considered as an overheated mode. For the 1% duty cycle it was demonstrated that the CCT was tuneable in three times by modulating input current and pulse width (Fig. 2). It has also been demonstrated that there is a possibility of keeping luminous flux independent of pulse width variation for a constant value of current pulse (Fig. 3)

Deep green and monolithic white LEDs based on combination of short-period InGaN/GaN superlattice and InGaN QWs

International audienceThis work presents the results of the investigation of approaches to the synthesis of the active region of LED with extended optical range. Combination of short‐period InGaN/GaN superlattice and InGaN quantum well was applied to extend optical range of emission up to 560 nm. Monolithic white LED structures containing two blue and one green QWs separated by the short‐period InGaN/GaN superlattice were grown with external quantum efficiency up to 5–6%

Dependence of the efficiency of III-N blue LEDs on the structural perfection of GaN epitaxial buffer layers

cited By 2International audienceIII-N blue LED structures with active regions based on InGaN nanoislands are studied. The structures are grown by metalorganic vapor-phase epitaxy (MOVPE) on GaN layers deposited by various methods for the initial formation of an epitaxial layer. It is shown that, due to strong carrier localization in narrow-gap InGaN nanoislands, the electroluminescence efficiency is independent of the crystal perfection of the material

Effect of stimulated phase separation on properties of blue, green and monolithic white LEDs

International audienceDifferent methods of stimulation of phase separation in an InGaN QWs by technological methods and by design of structure were investigated. Effect of admixing of hydrogen during growth interruptions (GIs) after deposition of the InGaN QWs on their structural and optical properties and properties of InGaN‐based LEDs was investigated. Effect of growth pressure on the phase separation was investigated and formation of separate InGaN islands at increase in growth pressure was revealed. It was shown that the phase separation is stumulated in composite InAlN/GaN/InGaN heterostructures and formation of well isolated InGaN islands was observed. Effect of the phase separation on the properties of the blue and deep green LEDs was investigated and strong changes in the spectral position and current dependence of the quantum efficiency were revealed. It was shown that formation of the island due to the phase separation allows control position and width of the emission line and maximum in current dependence of the quantum efficiency. Monolithic white LEDs are containing in active region blue and green InGaN QWs grown with applying of the GIs and emitting in spectral range from 440 nm to 560 nm were studied. Monolithic white LEDs having optimal design of active region demonstrate CCT in the range of 9000‐12000 K and maximal external quantum efficiency up to 14 lm/W